The goal of a paper path system in a typical xerographic printing system is to transport media from a feeding unit in synchronism with a moving image bearing photoreceptor surface. The movement of the media to a transfer zone necessarily must arrive at the transfer zone at a given time and with a given velocity to match the velocity of the image bearing photoreceptor surface. Prior art systems are often open loop systems with the media running at a specific speed and position adjustment being made at a transfer registration station just prior to transfer. A difficulty with such systems is the often erratic and abrupt adjustments that must be made at the registration station due to the unpredictability of photoreceptor and media drives and the uncertainty of the position of the image on the photoreceptor. With little time and space for adjustment, the correction can be erratic. This is particularly true in higher speed, higher volume machines.
It is known in the prior art, for example, U.S. Pat. Nos. 5,328,168 and 5,257,070 to selectively activate copy sheet drives after a machine jam in order to position copy sheets for favorable jam clearance including the steps of maintaining a predetermined interdocument space between copy sheets and systematically purging copy sheets from zones of the paper path in a predetermined order.
A difficulty with these prior art systems, however, is the restriction of the systems to jam recovery. Other prior art systems are inadequate to provide for a smooth flow of copy sheets to a registration station, but require relatively abnormal and uncertain adjustments within a relatively narrow adjustment time frame and space. It would be desirable, therefore, to provide a relatively smooth and more accurate adjustment technique over the entire paper path to synchronize the arrival of copy sheets and images on a photoreceptor at an image transfer station.
It is an object of the present invention, therefore, to treat the paper path as a sequence of separate paper path modules and to impose restraints upon the modules dependent upon the placement of copy sheets within the modules. It is another object of the present invention to move copy sheets within the same module at the same velocity and to synchronize the velocity of modules sharing communication with the same copy sheet. It is still another object of the present invention to adjust spacing between copy sheets only when one of the copy sheets is not in a transition zone between two modules. Further advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.